1. Technical Field of the Invention
The present invention relates generally to sensor arrays, and specifically to optical multiplexers for directing light toward the sensor arrays.
2. Description of Related Art
Biochemical sensors based on fluorescence are used for many different types of analytes of physiologic interest. For example, fluorescence-based blood analyzers that measure blood gases, electrolytes, metabolites, coagulation state and immunological markers are commercially available. The ability to measure multiple analytes in parallel is generally useful for the diagnosis of a patient""s state of health. To measure multiple analytes in parallel requires an array of biochemical sensors and an optical device to excite and read the array.
Current optical devices measuring fewer than ten biochemical sensors often have a dedicated optical source for each sensor. As the number of biochemical sensors increases, it becomes advantageous to share device hardware, especially illumination hardware, for multiple sensors. The ability to share illumination hardware is especially important when the optical device is a small, handheld device.
One possible solution involves translating the biochemical sensors on a mechanical stage. However, this approach is overly complicated and expensive for a small, handheld optical device. Alternatively, the light source can be directed or steered using either a single moving mirror, or a micromirror array, as described in U.S. Pat. No. 5,061,049, which is hereby incorporated by reference. However, existing moving mirror devices require a large spatial separation between the mirror and the sensor plane, which increases the thickness of such devices beyond what is feasible for a small, handheld optical device.
The present invention is directed to a micromirror array for use within an optical multiplexer. The micromirror array includes a top face and at least one side face. Pivotable micromirrors of the micromirror array are arranged in a multiple row, multiple column format on the top face. In addition, each of the side faces of the micromirror array has at least one row of pivotable micromirrors. In operation, a first micromirror on one of the side faces of the micromirror array is capable of redirecting light propagating substantially parallel to the side face towards the top face. A second micromirror on the top face redirects the light propagating parallel to the top face to exit the micromirror array.
In one embodiment, the optical multiplexer including the micromirror array steers light from a single source onto multiple, coplanar sensors for the purpose of exciting fluorescence. Thus, by pivoting one side face micromirror and one top face micromirror, a light source entering at one corner of the micromirror array can be directed to exit near normal incidence anywhere on the bottom of the device. In other embodiments, this approach can be extended to direct light from more than one source. For example, as many as eight sources, two per corner, can be directed (provided that the side face micromirrors pivoted xc2x145xc2x0 about their vertical centerlines and the top face micromirrors pivoted above xc2x145xc2x0 about their two orthogonal centerlines).
The micromirror optical multiplexer can be implemented within a small, handheld optical device capable of reading fluorescence from multiple biochemical sensors. Advantageously, the small, handheld optical device can be made compact with a flat form factor (i.e.,  less than 10 mm thick). Moreover, when making fluorescence measurements on a sample of blood, it is preferred that neither the excitation nor the emission light pass through the blood to avoid known autofluorescence of certain plasma proteins and scattering from the red blood cells. Therefore, the micromirrors of the top face of the micromirror array are preferably dichroic mirrors, which allow the illumination of a biochemical sensor with excitation light and the collection of the resultant fluorescent light from the same side of the sensor.